Problem: 2 notebooks cost $1.94. Which equation would help determine the cost of 4 notebooks?
There are several equations that could help determine the cost, each with a slightly different approach. If we let $x$ represent the cost of 4 notebooks, we have the following proportion: $\dfrac{x}{4}$ We have to pay $1.94 for 2 notebooks, and that can be written as a proportion: $\dfrac{\$1.94}{2}$ Since the price per notebook stays the same, these two proportions are equivalent. $\dfrac{x}{4} = \dfrac{\$1.94}{2}$